This invention relates to apparatus for continuously depositing weld metal on a dished surface and more particularly to cladding the inside surface of heads for pressure vessels.
It is economical to form heads for large pressure vessels of carbon steel and then coat or clad the surfaces with stainless steel or other corrosion resistant materials in order to meet the requirements of the nuclear power or chemical industry. Large, high pressure, pressure vessels require thick heads that cannot be economically produced solely from corrosion resistant materials so that coating the surfaces with a corrosion resistant material or cladding them is the only economical method of producing such equipment. The cladding must be free of defects and continuous so as not to produce stress concentrations or areas where corrosion can attack the base metal.
Explosive techniques have been utilized to metallurgically bond sheets of corrosion resistant material to the dish-shaped heads. However, the bond between the base metal and the protective sheet is difficult to perfect as it must stand up to repeated temperature and pressure cycling. Cladding utilizing welding techniques has been utilized successfully; however, the cladding has been deposited by forming a series of concentric rings. The operator stops the welding process and restarts it to form each new ring. The setup time between rings is relatively large, thus reducing machine utilization time. The machines are large and expensive, therefore, improving their utilization efficiency is financially beneficial.